Publication Date:
2017-04-04
Description:
Seismograms from 55 intermediate-depth Vrancea earthquakes (M 4:0–
7:1) recorded at 43 stations of an accelerometric network in Romania are used to
derive source spectra and site amplification functions from S waves in the frequency
range 0.5–20 Hz with the generalized inversion technique (GIT) (Castro et al., 1990).
Attenuation is taken into account using the nonparametric attenuation functions derived
by Oth et al. (2008) from the same dataset, and the attenuation-corrected data are
then split into source and site contributions. The source spectra follow the ω 2 model
(Brune, 1970, 1971) with high corner frequencies and a related Brune stress drop of
the order of 100 MPa. The site amplification functions are separately determined for
both horizontal and vertical components. Contrary to widespread expectation, the
vertical component shows significant amplification effects at high frequencies. The
H=Z ratios determined from the GIT results compare well with H=V ratios computed
directly from the S-wave window of the accelerograms (Lermo and Chávez-García,
1993). The basic assumption for the determination of site effects from H=V ratios is
that the vertical component is not or only little affected by site effects. For Vrancea
earthquakes, this assumption is incorrect; consequently, site effects should not be
estimated from H=V ratios. The reason for this peculiar fact is the geometry of
intermediate-depth seismicity that leads to almost vertical ray paths beneath the
stations.
Description:
Published
Description:
235-254
Description:
4.1. Metodologie sismologiche per l'ingegneria sismica
Description:
JCR Journal
Description:
open
Keywords:
source spectra
;
Vrancea region
;
site effects
;
04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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